1. Field of the Disclosure
The present invention relates to a thin film transistor substrate and method for fabricating the same that secures an alignment margin and reduces the number of mask steps.
2. Discussion of the Related Art
Liquid crystal display (LCD) devices, one of flat panel display devices for displaying images by using liquid crystal, are widely used throughout the industry in general owing to various advantages such as thin profile, lightweight, a low driving voltage and low power consumption compared to other display devices.
LCD devices are provided with a liquid crystal panel having a matrix of liquid crystal cells and a driving circuit for driving the liquid crystal panel. The liquid crystal panel has a thin film transistor substrate and a color filter substrate arranged opposite to each other with liquid crystal disposed therebetween. Formed on an upper substrate, the color filter substrate has a black matrix for preventing light from leaking, a color filter for producing a color, a common electrode for forming an electric field with a pixel electrode, and an upper alignment film formed over the above elements for the alignment of the liquid crystal.
The thin film transistor substrate has gate lines and data lines formed on a lower substrate, a thin film transistor formed at every crossing portion of the gate lines and the data lines as a switching device, a pixel electrode formed for each liquid crystal cell and connected to the thin film transistor, and an alignment film coated over the above elements. The thin film transistor supplies a pixel signal from the data line to the pixel electrode in response to a scan signal supplied to the gate line.
The thin film transistor substrate of the liquid crystal panel requires a plurality of mask steps, which makes the fabrication process complicate and thus increases the production costs. That is, because each mask step includes a thin film deposition step, a washing step, a photolithography step, an etching step, a photoresist peeling off step, an inspection step and so on, the production costs increase. Of these steps, the photolithography step requires an expensive equipment due to a high alignment accuracy requirement. When a misalignment occurs during the photolithography step, the misalignment directly causes a defect. In particular, because the gate lines, the data lines and the pixel electrodes are formed by different mask steps, a probability of misalignment is very high during the photolithography process.
Consequently, efforts are being made to reduce the number of mask steps required for fabricating a thin film transistor substrate and thus reduce the production costs.